Non-destructive evaluation (NDE) techniques are techniques or methods for testing or inspecting an object or material without damaging or alternating the object or material and are often preferred in measuring and evaluating structural and other properties of objects and materials.
Some examples of existing NDE techniques to inspect fiber reinforced polymer (FRP) composite materials are ultrasonic testing (UT), X-ray radiography and tomography, infrared (IR) thermography or digital image correlation (DIC) with visible range radiation. Depending on the need or requirements of a particular application, each of these methods may have its own advantages and limitations.
For example, a phased array UT may be used to furnish precise information about the location of damage and its spatial distribution inside a glass fiber reinforced polymer (GFRP) laminate structure. However, phased arrays require coupling with the test specimen, and they can be rather complex and costly because sophisticated electronics are needed to adjust the time delays between the piezoelectric transducers for proper focusing of the wave energy at the defect site. Hence, relatively simpler systems for immersed and air coupled UT with a single transducer have been routinely used for NDE of composite structures.
For another example, X-ray computed tomography (CT) can provide detailed images of delaminations and other defects in composites. However, X-ray CT uses relatively high levels of ionizing radiation, which can be dangerous for inspectors. Moreover, chamber volume for X-ray CT severely limits the size of the sample which can be evaluated.
IR thermography may be suitable for rapid screening of large components, but it provides little information about the volumetric distribution of damage.